Abstract

The origin of rare-metal deposits in granites is considered with regard for experimental data, which place constraints onto interpretations of geological materials and the genetic models. The role of both magmatic and hydrothermal–metasomatic factors in the formation of various types of rare-metal deposits is discussed. The saturation concentrations of Ta and Nb in granite melt significantly depend on the melt composition and vary from ~2–5 to ~0.1 wt %. These concentrations depend much less significantly on temperature and pressure. In granite melt in equilibrium with fluorine-bearing fluid, Ta and Nb are strongly partitioned into the melt. The paper demonstrates principal difference in the partitioning of W and Ta, Nb, Sn in melt granite–salt systems. The fluoride water–salt phase is a very effective extractant of W, while Ta, Nb, and Sn are completely retained in the aluminosilicate melt. The model magmatic fluid in equilibrium with Li–F granite melt is multiphase and contains significant amounts of SiO₂ and Na, Al, Li and K fluorides. The solubility of ore minerals in this fluid is insignificant, with the concentration of Nb much higher than that of Ta. The HF concentrations in high-temperature magmatic fluids were estimated at ~0.5–1 M HF. The experimentally determined solidus temperatures of Li–F granites are ~570–630°C at a pressure of 100–200 MPa. At T = 300–550°С and P = 50–100 MPa, the actual hydrothermal transfer of Ta and Nb is possible only with sufficiently concentrated HF and, possibly, KF solutions (fluids). In sodium alkaline solutions, hydrothermal transport is quite probable for Nb but difficult for Ta, and the pyrochlore solubility is thereby higher than that of columbite.

中文翻译：

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含氟花岗岩系统中稀有金属沉积过程的理化参数：实验数据

摘要

考虑到实验数据，考虑了花岗岩中稀有金属矿床的起源，这些数据对地质材料和遗传模型的解释施加了限制。讨论了岩浆和热液-交代作用因子在各种类型的稀有金属矿床形成中的作用。花岗岩熔体中Ta和Nb的饱和浓度显着取决于熔体成分，范围为〜2–5至〜0.1 wt％。这些浓度对温度和压力的依赖性小得多。在与含氟流体平衡的花岗岩熔体中，Ta和Nb强烈地分配到熔体中。该论文证明了在熔融花岗岩-盐体系中W和Ta，Nb，Sn分配的主要区别。氟化物水盐相是W的非常有效的萃取剂，而Ta，Nb，Sn和Sn完全保留在铝硅酸盐熔体中。与Li–F花岗岩熔体平衡的模型岩浆流体是多相的，并且包含大量的SiO₂和Na，Al，Li和K氟化物。矿石矿物在该流体中的溶解度微不足道，Nb的浓度远高于Ta。估计高温岩浆液中的HF浓度约为0.5-1 M HF。实验确定的Li–F花岗岩的固相线温度在100–200 MPa的压力下约为570–630°C。在T = 300–550°С和P = 50–100 MPa时，只有在足够浓缩的HF和KF溶液（流体）的情况下，Ta和Nb的实际水热传递才可能发生。在钠碱溶液中，Nb很有可能发生水热传输，而Ta则很困难，因此，烧绿石的溶解度高于co石的溶解度。